Amid a worsening flu outbreak at Lackland Air Force Base in San Antonio, Texas, the U.S. Air Force, Army and Navy are once again requiring new recruits to get vaccinated against the influenza virus, according to ABC News. The move comes two months after Defense Secretary Pete Hegseth rescinded the U.S. military’s mandate that they do so.

As of June 23, 2026, at least 222 recruits on the base have fallen ill and four have reportedly been hospitalized.

In his April 21 announcement making the flu vaccine optional, Hegseth cited medical autonomy and religious freedom, describing the vaccination requirement as “overly broad and not rational,” telling troops that “your body, your faith and your convictions are not negotiable.”

The flu shot requirement that Hegseth ended had been in place since 1945, with one brief pause in 1949. It was part of a tradition of military vaccine mandates nearly as old as the United States itself.

As an epidemiologist who studies vaccine-preventable diseases, I found the end of the flu mandate striking less for its immediate impact than for what it signals. For most of American history, military commanders took for granted that infectious disease could cost them a war, which is why vaccination was considered a matter of military readiness rather than personal choice.

The Lackland outbreak is evidence that the underlying epidemiology has not changed – only the political climate surrounding public health.

A tradition that started with George Washington

The first American military vaccine mandate predates the Constitution. In the winter of 1777, Gen. George Washington ordered the mass inoculation of the........

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